The IR optical transport system will be designed to handle beam
powers of up to 5 kW to allow for future growth capability.
Full-power output should be directable to any one of the six user
areas provided the appropriate interlock chains are engaged. In
addition, low-power pickoffs will be provided to each or any area
simultaneously with high power to a different area.
Power pickoff will be fail-safe with full power capability in
an integral optical dump. Optical dump shall exhibit less than
10-4 backscatter into any occupied area. This is necessary
for operational safety.
FEL optical diagnostic monitoring shall be provided consisting
of a power monitor, a wavelength monitor, a pulse length monitor,
and an image of the transverse beam profile at an appropriate
pickoff point. Data from these will be provided for each user
area and the FEL control room to optimize the FEL operation for
Low-power pickoff will provide 10-3 power to all user
areas simultaneously. A low-power (5 mW) HeNe beam collinear
with anticipated FEL beam will also be provided.
Pressure is to be better than 10-4 torr. Quick vacuum
reconnects are to be used in user areas. This is set by need to
avoid absorption on atmospheric molecular lines.
An interlock is to be provided on each user lab door, with logic
separately in each area. Redundant fail-safe shuttering control
is to be provided. Master enable is to be provided by the FEL
Outcoupling to room air is to be with a Brewster window of CaF2.
Transport shall not degrade overall beam quality by more than
0.1 times diffraction limit. This requirement is easy, provided
mirror absorption is not large and if the number of bounces is
minimized (<6). Large optical trains can provide modest beam
distortions if care is not taken. At the longest wavelengths diffraction
will pose a problem in achieving this goal. Mirrors must be at
least 5 optical waists in diameter.
This is necessary to minimize spurious losses in the system and
reduce what is available to users. In the IR region it should
be easy to keep losses to <20% given the good reflectivities.
An exception might be at the longer wavelengths where diffraction
could cause added losses if care in the design is not taken.
Remote alignment will be provided to set up the transport and
optimize it during laser operation. A range of 1 mrad in both
directions is generally sufficient to deal with unexpected mounting
Spurious Optical Modes
Scatter, etc., shall be held to better than 10-3 out
of the user aperture in order to minimize safety issues and provided
a reasonable degree of user control on process variables.
Mode Size, Configuration
The mode will be Gaussian with a radius ranging from 1.016 - 1.83
The beam will be imaged at infinity. The Rayleigh range will be
in excess of 150 m.